The equipment proposed in publication CN201470294 U for producing nitrogen utilising pressure swing adsorption is known in the prior art. In pressure swing adsorption, adsorption of gas in an adsorption medium is effected by increasing pressure, whereupon gas to be separated adsorbs in the composition of the adsorption medium. Gas adsorbed in the adsorption medium can be separated from the adsorption medium by decreasing the pressure of the adsorption column and by applying a vacuum in the adsorption column, whereupon the adsorption medium is simultaneously regenerated. The technology based on pressure swing adsorption is generally known as PSA technology (Pressure Swing Adsorption).
Processes based on the PSA technology generally use cyclic pressurisation, wherein several adsorption columns connected in series are run in different stages of pressure swing adsorption. When the gas to be separated has been adsorbed in the adsorption medium, it is possible, under high pressure, to start discharging unadsorbed gas from the adsorption column simultaneously feeding a new gas mixture to the adsorption column, until the carbon molecular sieve becomes saturated by adsorbed gas or gases. After this, the flow of the gas product is stopped by closing the valve to the gas product line and the venting of the adsorption column is started into the following columns connected in series. Finally, the pressure of the adsorption column decreases to the level of air pressure, but a significant part of the adsorbed gas is adsorbed in the adsorption medium. With a vacuum, adsorbed gas can be made to desorb from the adsorption medium and thus recovered, at the same time regenerating the adsorption medium. The same vacuum is also used to remove moisture from the adsorption medium.
However, the prior art cyclic feeding described above between adsorption columns requires a notable number of operation valves and a control unit in order that the feeding of a gas mixture from one adsorption column to another can be correctly scheduled and gas product waste can be minimised. In addition, the high pressure applied in adsorption sets its own requirements to adsorption columns, which must meet the pressure vessel requirements. In turn, this causes additional costs related to the manufacture of a pressure vessel.
Due to the facts set forth above, small-sized scalable systems are not available on the market, but only large systems that are poorly applicable to different capacity needs. In the publication CN201470294 U, attempts have been made to solve the problem related to capacity by using smaller standard size adsorption columns connected in parallel in the same feed or discharge line. In this way, capacity can be increased or decreased by changing the number of adsorption columns connected in parallel. By using an adsorption column of one size, manufacturing costs of adsorption columns of different sizes are avoided. However, a problem related to this kind of construction is that specific operation valves and controls have been manufactured for each adsorption column separately in each size class, which makes the system expensive to implement.
Publication U.S. Pat. No. 5,549,736 proposing an adsorption column set meant for pressure swing adsorption is also known in the prior art. In this adsorption column set, custom-built adsorption columns are arranged in series and additional adsorption columns are provided alongside with these adsorption columns to increase capacity. However, such an adsorption column set is expensive to manufacture, since each adsorption column and additional adsorption column has its own operation valves and controls. In addition, the connection of additional adsorption columns requires a custom-built construction.